Employee Benefit Plans (Net Periodic Benefit Cost (Credit)) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 43	$ 40
Interest cost	91	101
Expected return on plan assets	(193)	(177)
Amortization of net actuarial loss	49	39
Settlements		2
Net periodic benefit cost (credit)	(10)	5
Pension Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	4
Interest cost	3	8
Expected return on plan assets	(14)	(39)
Amortization of prior service credit	0	0
Amortization of net actuarial loss	2	5
Net periodic benefit cost (credit)	(8)	(22)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	7
Interest cost	15	17
Expected return on plan assets	(39)	(33)
Amortization of prior service credit	(12)	(13)
Amortization of net actuarial loss	1	4
Net periodic benefit cost (credit)	(28)	(18)
Other Postretirement Benefits | Dominion Energy Gas Holdings, LLC
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	1	3
Expected return on plan assets	(5)	(7)
Amortization of prior service credit	(1)	(1)
Amortization of net actuarial loss	0	1
Net periodic benefit cost (credit)	$ (4)	$ (3)